Industry requires standard blank tubes to be formed into one-piece tubular shapes. The general operations of bending, stretching, depressing and radially, expanding a tube blank, with or without a mandrel, are known. Some metals and alloys are formed into complex tubular shapes by a hydroforming process. The hydroforming process requires several steps to form the desired tubular shape. See, e.g., U.S. patent application Ser. No. 08/856,511, filed May 15, 1997, and assigned to the assignee of the present application, said application being incorporated herein by reference in its entirety. Generally, a tube or workpiece is placed between a pair of dies having cavities that define the desired resultant shape of the tube. The dies merge, and the ends of the workpiece are sealed with a pair of sealing units. The workpiece is filled with fluid which is then pressurized. Pressurizing the fluid within the workpiece results in expanding the workpiece to conform to the cavity shape. The fluid is drained from the workpiece and the sealing units are removed to release the workpiece. The main problem with this process is that hydroforming presses are extremely expensive. A single hydroforming press can cost approximately three million dollars.
Since mechanical or hydraulic presses are widely available and have been in service in many factories for years, attempts have been made to modify these presses to perform the above hydroforming operation. The problem with prior attempt to perform hydroforming operations on mechanical or hydraulic presses is that several additional pieces of equipment are required in order to make the hydroforming operation work. Such equipment may include, for example, external water units, external hydraulics and additional fittings, hoses and valves. This increases the cost and decreases the reliability of the hydroforming operation.
The present invention is directed toward eliminating some of the additional equipment required to perform a hydroforming operation.